1. Field of the Invention
The invention relates to semisolid polymerizable unsaturated polyester resin syrup compositions, to methods of making such compositions, to methods of curing such compositions and to the thermoset products obtained by polymerizing such compositions.
2. Description of the Prior Art
Unsaturated polyester resin syrups have been employed in the production of a wide variety of products. See Polyester Resins and Their Applications, Bjorksten et al, Reinhold Publishing Company, New York, 1960 (Fourth Printing). The unsaturated polyester resin syrups customarily are reinforced with fibrous fillers such as glass fibers and also are extended with inert particulate fillers such as wood flour, silica, ground glass, clay, calcium carbonate, and the like. Typical end products include flat and profiled building sheets, automobile components, furniture, plumbing fixtures, ductwork, boats, electrical housing components, electrical circuit boards and the like.
Copending application Ser. No. 544,966, supra, describes compositions containing unsaturated polyester resin syrups and aqueous sodium silicate which thicken and remain polymerizable until exposed to polymerizing conditions. In a preferred embodiment of my prior process, the unsaturated polyester resin syrup and the aqueous sodium silicate are combined and polymerized concurrently. In a further embodiment of the earlier invention, the aqueous sodium silicate and unsaturated polyester resin syrup are combined, with or without fillers, and allowed to thicken for subsequent reuse. One typical reuse is in the form of molding powders where the thickened mixtures are ground, chopped or pulverized for subsequent molding.
One of the shortcomings of the polymerizable mixtures is that the requirement for thickening establishes some restraints on the ratio of aqueous sodium silicate and unsaturated polyester resin syrup which may be combined for developing specific thickening characteristics. The act of mixing the unsaturated polyester resin syrup with the aqueous sodium silicate brings about changes in the composition of both the aqueous sodium silicate and the unsaturated polyester resin syrup. Specifically the aqueous sodium silicate forms, at least in part, a hybrid silica gel. The unsaturated polyester resin syrup has its carboxylic end groups converted to carboxylate salts of sodium. Some quantities of free water are released in the resulting system. The resulting material is not an emulsion but instead appears to be a mixture of the ingredients.
The mixture may harden rapidly or slowly to a final consistency depending upon the ratios of aqueous sodium silicate and unsaturated polyester resin syrup. There is a need for regulating the thickening rate and final consistency of such mixtures. Rapid thickening is particularly desirable when manufacturing sheet molding compounds, bulk molding compounds or molding powders.